pkey/rsa_genkey: Remove commented out code
pkey/rsa_genkey: Remove commented out code

There is some commented out X.509 certificate writing code present in
rsa_genkey. It looks like it has been commented out since the beginning
of time. Let's remove it, since commented out code is not in good style.

Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls